This invention regards a dynamic damping device for use in a drill string, designed especially for use when drilling for hydrocarbons in sedimentary rocks.
Known dynamic dampers are extensively used to dampen oscillations that arise in mechanical constructions subjected to variable loads. In a drill string having a length of several thousand metres, oscillations can arise as a result of variations in the torque along the drill string.
Variations in torque may be due to different frictional conditions along the string and drilling through formations of different hardness, causing the moment on the drill bit to vary. Such uncontrollable variations in torque will in turn generate oscillations that exert great forces and vibrations on the drill string, in particular when the oscillations resonate with the natural oscillations of the drill string.
The use of more modern and more powerful rotary machines over the last years has resulted in the drill string now being subjected to considerably greater strain, with a consequent increase in the risk of damage caused by uncontrolled oscillations and vibrations.
A particular problem arises when the drill bit hits a formation that is difficult to penetrate, and jams. The drill string is turned by torque from the drilling machine on the surface, and the string builds up energy which is released when the drill suddenly breaks loose. All the stored energy is released through uncontrolled rotation, and the lower part of the drill string may reach extreme rotational speeds that can cause damage to the drilling equipment. Today's controlled drilling systems include a lot of electromechanical equipment that is especially susceptible to damage when subjected to this type of strain.